The present invention relates to chipper apparatus, and more particularly to an improved chipper-head structure which affords both maximum desired guidance of a log as it passes through a chipping station, and positioning of a rotary chipper head in a manner which eliminates undesirable "back cutting".
Over the years, many improvements have been made in wood-processing equipment to maximize commercial yields from logs. One such improvement is the well-known chipper head which produces a planar surface along a side of a log, with usable chips removed from the periphery of a log.
Considerations which are especially important, relative to the efficient performance of a chipper head, are (1) that it produce a smooth, uniform surface on the face of a chipped log, and (2) that a log, as it passes such a head, be well supported so that it doesn't "chatter" or "wander".
While there are many commercially available chipper-head structures that do reasonably well at achieving these ends, those in the industry recognize that there is still much room for improvement. For example, where a chipper head is oriented to produce a "cutting plane" which parallels a log's transport path through a chipper, a frequent problem is one referred to above as "back cutting"--a phenomenon resulting from the fact that, during the downstream sweep of a chipper-head's knives, the knives recontact the log's now-flat surface, marring it, and thereby removing material which should not be removed.
An important approach to eliminating the problem of back cutting has been to position a chipper head with its cutting plane at a slight angle relative to a log-transport path so that the upstream sweep of its knives produces the desired chipping and surface-facing action, but also so that the downstream sweep results with a knife distanced from the passing log surface. Here, however, the problem has existed of how adequately to support the face of a log against chatter, etc., where only the lead, or upstream, portion of a chipper head contacts a log.
A general object, therefore, of the present invention is to provide unique chipper apparatus which takes care of these considerations and difficulties in a highly effective and simple manner.
More particularly, an object of the invention is to provide such apparatus wherein a rotary chipper head is so mounted that, when rotating, its knives define a cutting plane which is at a slight angle (downstream divergent) relative to the transport path of a log through the apparatus, with guide structure also provided, centrally relative to the rotary axis of the head, defining a guide plane which substantially parallels the log-transport path.
According to a preferred embodiment of the invention, a rotary chipper head, carrying the usual complement of chipper knives, is secured to one end of a hollow shaft which is journaled for rotation within a casing that is mounted on the frame of the apparatus. The mounting thus provided for the head is such that, when the head is rotated, the knives define a cutting plane which is at a slight angle (downstream divergent) relative to the transport path provided for a log through the apparatus. The axially outermost extremities of the knives, i.e. those ends which are closest to the transport path, describe what is referred to herein as a circularly bounded cutting expanse which is centered on the rotary axis of the head.
Supported on bearing structure within the hollow interior of the chipper-head shaft is a nonrotary shaft having one end anchored suitably to the apparatus frame, and its opposite end disposed within the chipper head for carrying a special guide plate. The guide plate herein described is circular (as viewed along the rotary axis of the head), and when viewed as one would see it looking down (in plan) on the log-transport path, has a wedge-shaped configuration. The perimeter of the guide plate lies within the circular boundary of the cutting expanse, and the face of the plate occupies and defines what is referred to herein as a "guide plane" which substantially parallels the log-transport path.
While, to suit different operating circumstances, the cutting plane and the guide plane can be arranged to intersect one another at different chosen locations, as will be explained below, in the preferred embodiment, these planes in the apparatus illustrated and described herein are arranged so that they intersect adjacent the most upstream extremity of the cutting expanse. The guide plate is mounted so that it will not rotate.
The various objects and advantages which are attained by the invention will become more fully apparent as the description given below is read in conjunction with the accompanying drawings.